The present invention relates to an electric actuator used in a drive system such as a power tailgate or power sliding door of an automobile.
Space and carrying capacity of an automobile are limited, so that it is requested to make such an actuator smaller and lighter with improvement in power output.
A conventional electric actuator comprises a motor casing having a motor; and a gear casing having a worm wheel and detachably connected to the motor casing. A motor shaft extends from the motor casing to the gear casing, and a worm is formed on the motor shaft in the gear casing to mesh with the worm wheel. The motor shaft is supported by three points comprising a base end portion of the motor casing, an intermediate portion of an iron core and a worm and the end of the gear casing as disclosed in JP2005-30545A.
However, in the bearing structure above, the end of the motor shaft is rotatably mounted in a hole of the gear casing to cause a slight gap between the motor shaft and the hole. During the rotation of the motor shaft, owing to reaction force of engagement of the worm with the worm wheel, the end of the motor shaft is likely to swing making the depth of engagement of the worm wheel decreased to cause damage to the worm wheel.
Furthermore, with swinging of the end of the motor shaft, the motor shaft moves axially. Especially, if the motor shaft is supported by a ball bearing at the intermediate part, an inner race of the ball bearing in which the motor shaft is pressingly fitted is subjected to thrust load to produce vibration or noise.
The base end of the motor shaft is rotatably supported by a bearing at the end of the motor casing to increase the length of the motor shaft by the part where the base end portion of the motor shaft is supported. Also, the end of the motor casing projects axially by forming a space for receiving the bearing to increase the axial length of the motor casing, expanding the size and weight to increase cost.